Gearbox

Gearbox /geer-boks/ noun (countable)

A gearbox, also known as a transmission, is a mechanical device that uses a set of gears to alter the speed and torque transmitted from an engine to the driven wheels. This is the box of cogs that translates the frantic, explosive energy of the engine into useful forward motion without everything immediately breaking. It is the essential intermediary, allowing a car to pull away from a standstill and to cruise at high speed without the engine screaming like a banshee. For generations of British drivers, the manual gearbox was a point of pride, a tool that separated a proper driver from a mere operator of a motorcar. The satisfying mechanical clack of a well-timed gearchange was a fundamental part of the driving experience, a pleasure now largely replaced by the seamless, soulless efficiency of the automatic.

The Full Story of the Gearbox

The internal combustion engine is a temperamental beast, only producing useful power within a narrow band of revs. The gearbox is its indispensable translator. It allows the engine's high-speed rotation to be converted into high-torque, low-speed rotation to get the car moving, and then into low-torque, high-speed rotation for cruising.

The earliest gearboxes were brutal, unforgiving things. Known as "crash" boxes because of the hideous grinding noise they made when a gearchange was fluffed, they lacked synchromesh. This meant the driver had to master the dark art of "double-declutching", a complex ballet of clutch and throttle used to perfectly match the speeds of the gears before they would engage. Announcing your arrival with a graunching gear change was a common form of public humiliation.

The arrival of synchromesh in the 1930s was a great leap forward for civilisation. This was a clever mechanism that acted like a small clutch on each gear, matching the speeds automatically and allowing for smooth, crunch-free shifts. It made driving accessible to everyone, not just the mechanically sympathetic.

While Americans quickly fell in love with the smooth, convenient, but dreadfully inefficient automatic gearbox, the British remained stubbornly attached to the manual. For sports cars and saloons of the 1950s and 60s, a popular and uniquely British feature was the overdrive. This was a separate, electrically-operated high gear, usually engaged with a flick of a switch on the gear knob. It allowed for relaxed, fuel-efficient motorway cruising and was a quirky halfway house between a four-speed and a modern five-speed gearbox.

The automatic was long viewed with deep suspicion in the UK, seen as a slushy, power-sapping American affectation. The British motor industry's own early attempts at small, automatic gearboxes were often so catastrophically unreliable they only confirmed the public's prejudice. Today, however, the battle is over. The traditional manual gearbox is a dying breed, replaced by modern, highly efficient automatics and dual-clutch systems that can change gear faster and more smoothly than any human ever could. The skill has been replaced by software.

For The Record

What is "double-declutching"?

It is the technique required to change gear smoothly on a non-synchromesh gearbox. It involves depressing the clutch, moving the lever to neutral, releasing the clutch, blipping the throttle to match engine revs to the new gear speed, depressing the clutch again, and finally selecting the gear. It was a complex but satisfying skill to master.

How did an overdrive unit work?

It was essentially a separate, two-speed planetary gearbox bolted to the back of the main gearbox. When engaged by an electrical switch, usually only on third and fourth gears, it would reduce the engine's RPM for a given road speed. This made for quieter, more fuel-efficient motorway cruising.

Why was the Mini's gearbox in the sump?

It was a core part of Alec Issigonis's revolutionary space-saving design. To create an incredibly compact power unit for the Mini, he placed the gearbox directly underneath the engine, with the two sharing the same oil. It was a brilliant piece of packaging, though it contributed to the Mini's famous gearbox whine.

Is a dual-clutch gearbox an automatic?

Yes and no. It operates automatically, without a clutch pedal, but mechanically it is more like two manual gearboxes working in parallel inside one housing. One clutch controls the odd-numbered gears and the other controls the even gears, allowing for incredibly fast, pre-selected shifts.

Why are manual gearboxes disappearing?

A combination of factors. Modern automatics are now often faster and more fuel-efficient than manuals. The rise of hybrid and electric cars, which don't require traditional multi-speed gearboxes, is also accelerating their demise. Above all, most buyers now simply prefer the convenience of an automatic for modern, congested driving.